Synthesis of ErFeAsO-based superconductors by hydrogen doping method

Here we demonstrate the technique to stabilize the ErFeAsO-based superconductor with the smallest lattice constants in LnFeAsO1-y (Ln = lanthanide) series using hydrogen doping method. Polycrystalline samples were synthesized by heating pellets with nominal compositions of ErFeAsO1-y (1-y = 0.75 ~ 0.95) sandwiched between pellets of LaFeAsO0.8H0.8 compositions at 1100 {\deg}C under a pressure of 5.0 - 5.5 GP. The sample with lattice constants of a = 3.8219 {\AA} and c = 8.2807 {\AA} shows the highest superconducting critical temperatures (Tc) of 44.5 K and 41.0 K determined by onset transitions of resistivity and susceptibility, respectively. We discuss phase diagram of Ln dependence of Tc in LnFeAsO-based superconductors.Comment: 12 Pages, 5 Figures, Accepted for publication in EP

Suppression of Magnetic Order by Pressure in BaFe2As2

We performed the dc resistivity and the ZF 75As-NMR measurement of BaFe2As2 under high pressure. The T-P phase diagram of BaFe2As2 determined from resistivity anomalies and the ZF 75As-NMR clearly revealed that the SDW anomaly is quite robust against P.Comment: 2 pages, 2 figure

Uniform Mixing of High-Tc Superconductivity and Antiferromagnetism on a Single CuO2 Plane in Hg-based Five-layered Cuprate

We report a site selective Cu-NMR study on under-doped Hg-based five-layered high-$T_{\rm c}$ cuprate HgBa2Ca4Cu5Oy with a Tc=72 K. Antiferromagnetism (AF) has been found to take place at TN=290 K, exhibiting a large antiferromagnetic moment of 0.67-0.69uB at three inner planes (IP's). This value is comparable to the values reported for non-doped cuprates, suggesting that the IP may be in a nearly non-doped regime. Most surprisingly, the AF order is also detected with M(OP)=0.1uB even at two outer planes (OP's) that are responsible for the onset of superconductivity (SC). The high-Tc SC at Tc = 72 K can uniformly coexist on a microscopic level with the AF at OP's. This is the first microscopic evidence for the uniform mixed phase of AF and SC on a single CuO2 plane in a simple environment without any vortex lattice and/or stripe order.Comment: 4 pages, 4 figures. To be published in Phys.Rev.Let

Microwave Penetration Depth and Quasiparticle Conductivity in PrFeAsO_1-y Single Crystals : Evidence for a Full-Gap Superconductor

In-plane microwave penetration depth $\lambda_{ab}$ and quaiparticle conductivity at 28 GHz are measured in underdoped single crystals of the Fe-based superconductor PrFeAsO$_{1-y}$ ($T_c\approx 35$ K) by using a sensitive superconducting cavity resonator. $\lambda_{ab}(T)$ shows flat dependence at low temperatures, which is incompatible with the presence of nodes in the superconducting gap $\Delta({\bf k})$. The temperature dependence of the superfluid density demonstrates that the gap is non-zero ($\Delta/k_BT_c\gtrsim 1.6$) all over the Fermi surface. The microwave conductivity below $T_c$ exhibits an enhancement larger than the coherence peak, reminiscent of high-$T_c$ cuprate superconductors.Comment: 4 pages, 3 figures. Version accepted for publication in Phys. Rev. Lett. For related results of hole-doped 122 system, see arXiv:0810.350